The Second Brain in the Gut, The Enteric Nervous System

In the last ten years a series of discoveries has changed our ideas about our mind/body connection. The evidence is building that one cannot distinguish the mind from the body, as previously thought. For example, with humans there is a second brain, complete with one hundred million neurons, which exists embedded in our intestines, known as the enteric nervous system. A bit of a surprise!

There is even a new field known as “Neuorgastroenterology” which studies the function and effects of the enteric nervous system. Does this second brain “help” us think? The early answer was no, but further studies have clouded the issue. Scientist have found that 90% of the information passing between the second brain through the first brain through the vagus nerve is information from the gut to the brain not the other way around. The enteric nervous systems use 30 neuro-transmitters, just as the brain does. This explains why we feel emotional moods in the gut. Irritable bowel syndrome actually arises from too much serotonin in the gut. To complicate matters even further – serotonin is the primary neuro-transmitter involved in mood regulation (think Prozac).

A recent study (Cryan JF, 2011) shows that the microbiota (actually foreign microorganisms that work in symbiosis, helping us digest our food) actually communicate with the brain and affect our behavior. Stress response, anxiety and depression have all been modulated by using mice bred not to accept certain bacteria in their gut.

This is only the beginning. This field has just begun to investigate the full effects of the enteric nervous system on our lives. The effects of these discoveries on how we think about traumatic brain injury rehabilitation, mental illness rehabilitation and the pharmacology of mental illness will be far reaching. It is strange and humbling to think that billions of non-human bacteria are having a say in how we feel and act. For more information see the Second Brain by Michael Gershon.